Interdecadal Variations In Winter Persistent Anomalous Cold Events Over Asian Mid-latitudes

Based on JHRA-55 daily reanalysis data and NCEP/NCAR reanalysis data,this study finds that after removing the linear trend in the surface air temperature,the frequency of persistent cold events from Lake Balkhash to Lake Baikal,Northeast China and Shandong Province exhibits an evident basically consistent interdecadal variation.During the 57-yr period,a subperiod from the mid-1980s to the late 1990s exhibits inactive characteristics compared with those before and after throughout the study period.According to the comparison analysis,both the averaged amplitude and total days of the persistent cold event over from Lake Balkhash to Lake Baikal have the larger value than the non-persistent cold event.In addition,the persistent cold event exhibit a more evident decadal variation.On the other hand,the averaged amplitude of persistent cold event over from the Northeast China and Shandong Province is generally weaker than the non-persistent cold event.In contrast to two other regions,the total days of all persistent cold events over Shandong Province are less than that of non persistent cold events.These findings indicate the distinct features of persistent cold events over the three different regions.On one hand,on a subseasonal timescale,the persistent cold events over the three different regions resemblance to each other,i.e.,the typical circulation patterns of persistent cold events are characterized by wave-train anomalies across the Atlantic Ocean and Eurasian continent,with significantly positive height anomalies that persist over the Ural Mountains and with significantly negative height anomalies that persist over the East Asia in the upper troposphere,positive SLP anomalies over Eurasian mid-to high latitudes and cold SAT anomalies from Lake Balkhash to Lake Baikal.On the other hand,the differences are that the centers of the circulation anomalies locate to a farther east location for the persistent cold events over the Northeast Asia and Shangdong Province.The circulation anoamlies for the persistent cold events over Shangdong Province,in addition,are elongated zonally to a much extent.The changes in background circulation at the interdecadal timescale correspond well with the typical circulation patterns at the subseasonal timescale,indicating their important role in modulating the frequency of persistent cxold events.Interdecadal changes in the background circulation can be partially explained by transient eddy feedback forcing,which is negatively correlated with the variance of high frequency transient wave activity and the surface air temperature.Further analysis showed that the average intensity and days of non persistent anomalous cold events did not show significant interdecadal variations compared to the persistent anomalous cold events.The relationships between the frequency of PCEs and the sea surface temperature and sea ice coverage are discussed in the last chapter.